Soda-lime glass, also called soda-lime-silica glass, is prevalent in the manufacture of glass containers and other glass products. Formation of the raw glass melt typically involves mixing the various glass-forming components at elevated temperature. The glass typically has a residence time in a furnace on the order of twenty-four hours to refine the glass by driving off gases and dissolving solids. The gases must be driven off ultimately to produce a solidified glass product without entrained gas bubbles; the process of removing bubbles in molten glass is called “refining.” In addition to being undesirably slow, this in-furnace process involves a large amount of space and high energy input.
A general object of the present disclosure is to provide a process for making soda-lime glass, which is more rapid and requires less energy input than conventional processes.
The present disclosure embodies a number of aspects that can be implemented separately from or in combination with each other.
A process for making soda-lime glass, in accordance with one aspect of the present disclosure, includes (a) forming sodium silicate glass in liquid phase and in the absence of water while releasing gaseous reaction products, and (b) mixing the sodium silicate glass reaction product of step (a) with other materials to form a soda-lime glass melt. The low viscosity of the molten sodium silicate glass (relative to or as compared with soda-lime glass at the same temperature) enables and promotes release of gaseous reaction products such as carbon dioxide.
A process for making soda-lime glass, in accordance with another aspect of the disclosure, includes calcining calcium carbonate in solid phase and at elevated temperature to form calcium oxide and release gases such as carbon dioxide. Sodium silicate glass is formed separately in liquid phase while releasing gaseous reaction products. The calcined calcium carbonate and sodium silicate glass intermediate products are mixed to form a soda-lime glass melt. Formation of sodium silicate glass as an intermediate product before mixing with the calcium oxide has the advantage of promoting release of gaseous reaction products in the sodium silicate glass due at least in part to the low viscosity of the sodium silicate glass (relative to or as compared with soda-lime glass at the same temperature). Thus, the calcium oxide intermediate product and/or the sodium silicate glass intermediate product is at least partially if not entirely refined, and at least partially if not entirely free of gases and gas bubbles, prior to the mixing stage. This greatly reduces the time and energy required for the final mixing stage to produce the soda-lime glass melt. The calcination step and/or the sodium silicate glass-forming step and/or the final mixing step can be carried out under reduced pressure further to promote release of gases and reduce bubble formation.
In one embodiment, the sodium silicate glass, is formed by melting soda ash in the presence of silica, releasing carbon dioxide gas. In another embodiment, the sodium silicate glass is formed by melting sodium chloride in the presence of silica and steam to form the sodium silicate and release hydrogen chloride gas.